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Abstract Glacial isostatic adjustment produces crustal deformation capable of altering the slope of the landscape and diverting surface water drainage, thereby modulating the hydraulic conditions that govern river evolution. These effects can be especially important near the margins of ice sheets. In Maine, USA, post-glacial changes in sedimentation within major river systems have been interpreted as the result of regional tilting and drainage rerouting due to glacial isostatic adjustment. In this study, we model isostatic adjustment driven by retreat of the Laurentide Ice Sheet, quantify the associated tilting and drainage rerouting, and explore how these changes impacted sediment transport in Maine's rivers. Through an analysis of changes to river slope and drainage area produced by glacial isostatic adjustment, we show that ice sheet retreat altered the median sediment grain size that rivers could entrain. We also find support for previous estimates of the timing and direction of drainage reversal at Moosehead Lake, Maine's largest lake. Our results suggest that the history of sedimentation in Maine's rivers reflects time-dependent effects of glacial isostatic adjustment that are superimposed on any changes in runoff associated with deglaciation. Further, our case study demonstrates that isostatic adjustment affects alluvial channel evolution and sediment delivery to the coastline for several millennia after an ice sheet retreats. 

Abstract The lateral migration of a river meander is driven by erosion on the outer bank and deposition on the inner bank, both of which are affected by shear stress (and therefore channel slope) through complex morphodynamic feedbacks. To test the sensitivity of lateral migration to channel slope, we quantify slope change induced by glacial isostatic adjustment along the Red River (North Dakota, USA and Manitoba, Canada) and two of its tributaries over the past 8.5 ka. We demonstrate a statistically significant, positive relationship between normalized cutoff count, which we interpret as a proxy for channel lateral migration rate, and slope change. We interpret this relationship as the signature of slope change modulating the magnitude of shear stress on riverbanks, suggesting that slope changes that occur over thousands of years are recorded in river floodplain morphology. 

Stories about the foundation of US geology as a discipline are prominent in the culture of field geology today. This article traces the threads of such “origin stories” through field geology practices and undergraduate training. The repetition of these origin stories obfuscates the colonial and race-fueled motives that underpin the actions of the US geologist characters featured in these stories. Increasingly, the field is recognized as a site of sexual and racial harassment and abuse. By making visible the racialized subplots in the history of US geology, which include entrenchment in racial science and land dispossession, I posit that the curated origin stories repeated today perpetuate processes of gendered and race-based exclusion and subjugation in field geology.